OpenGrok MCP Server

MCP server bridging OpenGrok search engine with AI for instant context across massive codebases

Overview

💡 Self-Contained Architecture: The VS Code extension includes the MCP server pre-packaged. You don't need Python, external Node.js installations, or complex environment setups. Just install and go.

Installation

Option 1 — VS Code Extension (Recommended)

Install OpenGrok MCP from the VS Code Marketplace, or search "OpenGrok" in the Extensions panel.

The extension provides a visual configuration UI and manages the MCP server process automatically.

Option 2 — npm / npx

Global install:

npm install -g opengrok-mcp-server
opengrok-mcp setup      # interactive wizard: URL, credentials, MCP client registration

Or run without installing:

npx opengrok-mcp-server setup

The wizard stores credentials securely in the OS keychain (macOS Keychain, Windows Credential Manager, Linux libsecret) with an encrypted file fallback for headless Linux.

Configuration Guide

1. Provide Connection Details:

   • After installation, the Settings panel will launch.
   • Input your OpenGrok endpoint, username, and password. Hit Save Settings. (Credentials are locked in your native OS keychain).
   • The plugin verifies the connection instantly. On your first run, VS Code will ask you to Reload the Window to register the MCP tools.
   • (Need to change this later? Use the OpenGrok: Manage Configuration command or click the gear icon in the status bar).

2. Activate the MCP Source in Copilot:

   • Launch the GitHub Copilot Chat window. Ensure you're using Agent mode.
   • Click the paperclip/tools icon (🔧) in the prompt box.
   • (If an Update Tools button appears, click it).
   • Locate OpenGrok in the list, check the box, and confirm.

⚠️ Note that VS Code manages tool authorizations per workspace. If you open a different repository, you may need to re-check the OpenGrok box in Copilot.

CLI Commands (v7.0+)

setup supports Claude Code CLI, GitHub Copilot CLI, and Codex CLI. VS Code is configured automatically by the extension — no CLI step needed. Credentials are stored in the OS keychain with an AES-256-GCM encrypted file fallback for headless/CI environments.

🔌 Third-Party Client Support

While tailored for VS Code, the integrated server logic runs perfectly with other agents natively supporting the MCP protocol, including:

Claude Desktop | Cursor IDE | Windsurf | Claude Code | Google Antigravity

👉 Refer to MCP_CLIENTS.md for configuration snippets and advanced daemon setups.

Prompting Examples

Talk to GitHub Copilot Chat naturally about your codebase:

Find the implementation of the render_pipeline function within the graphics engine project.

Retrieve the contents of /src/utils/math.cpp from line 450 to 520.

What is the definition of TextureManager? Please show me the header file declaration too.

Look for all places in the code where ThreadPool is instantiated or referenced.

Tool Reference

Primary Operations

🚀 Optimized Workflows (Compound Tools)

💡 These specialized tools merge multiple network requests into a single operation, reducing API chatter and cutting token usage by up to 90%.

(Note: The search functions support language filtering. Pass file_type as java, cxx, python, golang, etc.)

🔍 Investigation & Analysis Tools (v5.6+)

🧠 Memory Tools (Code Mode only, v5.4+)

🧬 Code Mode (v5+) — For Large Multi-Language Codebases

Set OPENGROK_CODE_MODE=true to switch to a 5-tool interface optimised for multi-step investigations:

All env.opengrok.* calls appear synchronous inside your code — the sandbox bridges async HTTP calls transparently using a SharedArrayBuffer + Atomics channel. Token savings of 80–95% are typical for complex investigations.

v9.0+ sandbox methods for interactive prompts and AI assistance:

When env.opengrok.search() returns zero results and sampling is available, _suggestions: string[] is automatically injected into the result — check it before calling sample() explicitly.

// Example opengrok_execute code
const refs = env.opengrok.search("handleCrash", { searchType: "refs", maxResults: 5 });
const first = refs.results[0];
const content = env.opengrok.getFileContent(first.project, first.path, {
  startLine: first.matches[0].lineNumber - 5,
  endLine: first.matches[0].lineNumber + 10,
});
return { callerFile: first.path, code: content.content };

The sandbox exposes a Living Document Memory Bank — two persistent markdown files that survive across turns:

Access via env.opengrok.readMemory(filename) / env.opengrok.writeMemory(filename, content) inside the sandbox, or via the opengrok_read_memory / opengrok_update_memory / opengrok_memory_status tools in classic mode. Delta encoding returns [unchanged] on repeated reads; richness-scored trimming keeps the most valuable log entries when space is tight.

Project Picker & Interactive Disambiguation (Elicitation)

When OPENGROK_ENABLE_ELICITATION=true, the server uses MCP Elicitation in two places:

1. Session start — opengrok_api (Code Mode) prompts the user to select a working project if no OPENGROK_DEFAULT_PROJECT is configured and more than one project exists.
2. Mid-execution — Sandbox JS can call env.opengrok.elicit(message, schema) to ask the user to choose between multiple matching files, revisions, or projects at any point during execution.

Requires a client that supports MCP Elicitation:

• Claude Code v2.1.76+ ✓

Enable in the VS Code configuration panel, or set OPENGROK_ENABLE_ELICITATION=true in your MCP client environment config. The server degrades gracefully to { action: "cancel" } on unsupported clients — no errors.

LLM Sampling

The server delegates LLM calls back to the client via MCP Sampling — using the client's model subscription without needing separate API keys. Used in three places:

1. Sandbox error explanation — When opengrok_execute code fails, sampling generates a concise explanation and fix suggestion.
2. Dependency graph summarization — Large opengrok_dependency_map graphs (>10 nodes) are summarized via sampling in legacy mode.
3. Zero-result query reformulation (v9.0+, Code Mode) — When env.opengrok.search() returns 0 results, sampling auto-injects _suggestions into the result object. Sandbox JS can also call env.opengrok.sample(prompt) explicitly for any AI-generated text.

Supported clients:

• VS Code Copilot ✓
• Claude Code — support pending (tracked in anthropics/claude-code#1785)

The server degrades gracefully when sampling is unavailable — sample() returns null, _suggestions is not injected.

VS Code Integration

Palette Commands

Core Settings Profile

Advanced Configuration (v7 — env vars)

For the standalone server (npx opengrok-mcp-server or Claude Code), set these environment variables:

Core Settings

Code Mode & Performance

Memory Bank

Rate Limiting

Response Cache

Security & Audit

MCP Protocol Features

OpenGrok API

HTTP Transport (v7.0+)

Logging

VS Code users can set opengrok-mcp.codeMode, opengrok-mcp.contextBudget, opengrok-mcp.memoryBankDir, opengrok-mcp.defaultProject, opengrok-mcp.responseFormatOverride, opengrok-mcp.compileDbPaths, opengrok-mcp.enableObservationMasker, and opengrok-mcp.observationMaskerTurns in VS Code settings instead.

MCP SDK Note: This version uses @modelcontextprotocol/sdk v1.29.0. MCP SDK v2 is in pre-alpha; we will migrate when stable (expected Q3-Q4 2026). v2 will enable enhanced completions for tool parameters and resource templates.

HTTP Transport (v7.0+)

By default the server communicates over stdio (standard MCP). For team deployments, you can also expose a Streamable HTTP endpoint:

OPENGROK_HTTP_PORT=3666 npm run serve
# or add to your MCP client config:
# "OPENGROK_HTTP_PORT": "3666"

Session Management

• Each HTTP client receives an isolated McpServer instance (per-session factory pattern)
• Sessions expire after 30 minutes of inactivity; OPENGROK_HTTP_MAX_SESSIONS caps concurrent sessions (default: 100)
• GET /mcp/sessions returns JSON with active session count and oldest session age

Authentication

Configure one of the following:

In resource server mode, this server validates JWTs issued by your own IdP — there is no built-in /token endpoint. RFC 9728 protected resource metadata is served at /.well-known/oauth-protected-resource.

RBAC Roles

Fail-safe: unknown or missing tokens default to readonly, not admin.

Security (v7.0+)

v7.0 includes a comprehensive security audit with the following hardening:

⚠️ v7.0.0 Breaking Changes

• OPENGROK_HTTP_CLIENT_ID and OPENGROK_HTTP_CLIENT_SECRET removed. Migrate to OPENGROK_JWKS_URI + OPENGROK_RESOURCE_URI for OAuth 2.1 (resource server model — bring your own IdP).
• Memory bank migrate() removed — the legacy 6-file layout is no longer supported. The 2-file layout (active-task.md + investigation-log.md) has been the default since v5.4.
• CORS is now allowlist-only when OPENGROK_ALLOWED_ORIGINS is set; unauthenticated wildcard CORS is disabled.

System Architecture

 [ AI Client ]                       [ Integration Layer ]                    [ Data Source ]
                              │                                 │
 +---------------+            │       +-------------------+     │      +----------------------+
 │ GitHub        │<──(stdio)──┼──────>│ OpenGrok MCP      │<────┼─────>│ OpenGrok REST API &  │
 │ Copilot Chat  │            │       │ Server (Node.js)  │HTTP │      │ Web Interface        │
 +---------------+            │       +-------------------+     │      +----------------------+
      │    ▲                           │          │
      │    │ (Configures & Hosts)      │    (Context Optimization)
      ▼    │                           │          │
 +---------------+                     │   o Context Fetch      │      +----------------------+
 │ VS Code       │                     │   o Multi-Search       │      │ Local File System    │
 │ Extension     │                     │   o Auto-Truncate      │<─────┤ (compile_commands) │
 +---------------+                     │                        │      +----------------------+

Building & Testing

# Initializing
npm install

# Code Quality & Tests
npm run lint           # Strict TypeScript & ESLint validation
npm test               # Execute the Vitest test suite (1113 tests)
npm run test:sandbox   # Sandbox integration tests (requires compile first)
npm run test:coverage  # Coverage report (≥89% threshold)

# Packaging
npm run compile   # Generate the esbuild artifact (includes sandbox-worker.js)
npm run vsix      # Create the downloadable extension file

We leverage GitHub Actions for automated CD. Tagging a commit (e.g., v1.2.3) automatically triggers the build matrix and attaches artifacts to a new GitHub Release.

For deep-dives into the architecture or PR guidelines, please read CONTRIBUTING.md.

Troubleshooting & Support

The MCP tools are missing in Copilot Chat

• Click the paperclip (🔧) icon to "Update Tools"
• Run Developer: Reload Window

"Connection failed" errors

• Double-check your OPENGROK_BASE_URL
• Make sure you aren't blocked by corporate VPNs/proxies

401 Unauthorized / Authentication failing

• Run the OpenGrok: Configure Credentials command to save your username/password again

Self-Signed SSL Certificates

• Turn off strict validation by setting opengrok-mcp.verifySsl to false

Slow queries or timeouts

• Limit the scope using the file_type argument or targeting a specific project
• OpenGrok might be indexing; run opengrok_index_health

Need verbose logs?

• Set the environment variable OPENGROK_LOG_LEVEL=debug to get extensive stdout trace data

OpenGrok Version Compatibility

License Information

This system is distributed under the PolyForm Noncommercial License 1.0.0.

• ✅ Permitted: Personal use, hobby projects, academic research, education
• ❌ Prohibited: Any commercial, business, enterprise, or paid utilization

Commercial Licensing: To use this extension in an enterprise context (internal tooling, CI pipelines, business infrastructure), a commercial license is strictly required. Reach out to [email protected] for enterprise tier pricing.

Read LICENSE-COMMERCIAL.md for full terms.